A known method for repairing a photomask is shown in the U.S. Pat. No. 4,340,654. This method includes the steps of coating a photomask having a transparent substrate with a material such as a starch polymer, the thickness of the coating being between 5 and 35 microns; directing a laser beam through the substrate of the photomask onto the coating so as to fuse the coating and substrate to form an opaque mixture thereof; and removing any unfused coating material from the photomask surface.
The technique suffers from several disadvantages. When fusing the coating and the substrate, the laser burns valleys into the substrate, damaging it. If any coating is fused to an area of the substrate where it is undesired, the coating cannot be removed. This method not only causes damage to the substrate, but can add unremovable defects to the photomask in areas where none existed before. Further, when using this technique one cannot demonstrate a resolution of 5 microns or less.